This study provides space use and movement information on mountain goats in the North Cascades Range that can be used to improve harvest management of fragmented and isolated populations. Our results suggest that Whitehorse and Three Fingers could be two distinct populations that do not intermix. Whitehorse mountain goats appear to be more vulnerable to human access and disturbance than the Three Fingers population based on spatial distribution and current known trail use and accessibility. Regardless of population size, the distribution and accessibility of each population could increase the vulnerability of overexploitation or extirpation with or without harvest.
Current Washington Department of Fish and Wildlife guidelines limit harvest to 4% or less in mountain goat populations with ≥ 100 animals within a contiguous area, with harvest rate reduction occurring if female removal exceeds 1.2% of the non-kid population during a 3-year period . This harvest strategy is based on previous studies that recommend managing mountain goat populations as a collection of smaller subpopulations with distinct female groups and males that may intermix [9, 33]. The sustainability of this approach is based on male-only harvest in populations that are ≥ 50 animals [2, 11, 40], but this harvest approach may be detrimental for smaller groups where population recovery is desired.
We found that 96% of locational fixes for mountain goats on Whitehorse occurred inside the harvest area boundary while only 10% of fixes for goats on Three Fingers occurred within the harvest area. This variance in habitat use indicates that there could be < 100 mountain goats in the contiguous area that is considered the BRNHA. The Three Fingers population utilization distribution is primarily outside the harvest area boundary. Given the variation in space use within the BRNHA, the majority of harvest pressure could be on the Whitehorse population, which is < 100 animals (3-year sightability x̄ = 66.33, σ = 14.01). Similarly, the Three Fingers non-kid population numbers have been consistently < 100 animals (3-year sightability x̄ = 53.00, σ = 12.53) and KDE core use analyses indicate primary distribution during the harvest season (September 1 – December 31) is outside the harvest area.
Our data indicated that the Whitehorse and Three Fingers populations were spatially separate and did not function as a classic metapopulation during our study period. While our sample size was limited, previous studies in the region support the need for understanding of mountain goat group interactions in hunted populations . We did not examine habitat patch use and habitat suitability within our study area in relation to spatial distribution. However, size and distribution of mountain goat habitat characteristics have been documented in Washington State [41, 42]. There was no visible explanation for population separation and lack of movement between Whitehorse and Three Fingers Peaks, although there were specific areas void of telemetry locations between the two populations. These areas did not appear to be different in terms of geology, landscape characteristics, or vegetation composition from adjacent areas occupied by collared mountain goats. While it is unclear how social dynamics and group size influence the spatial distributions of mountain goat populations, it is possible that social interactions could have influenced the spatiotemporal movement patterns of collared goats in our study area.
Unlike other ungulates, mountain goats do not preferentially seek out relatives to form subgroups [12, 43]. Adult female mountain goats maintain a stable and linear hierarchy and are often aggressive to each other during encounters [1, 44]. Avoidance behavior may keep adjacent populations from mixing and social organization can change rapidly over space and time . Furthermore, adult females typically display fidelity to their summer home ranges areas [45, 46]. We observed spatial separation with the adult male and levels of separation between collared females seasonally. Small mountain goat populations in rugged terrain may have more solitary individuals due to a reduced need for antipredator protection . These small populations could be subject to overharvest and eventual extirpation. Numerous studies have documented the mountain goat conservative life history strategy and sensitivity to over-harvest [11, 12]. Unlike other ungulates, mountain goats do not display compensatory breeding in response to harvest . In addition to harvest limits, hunter accessibility to small populations of mountain goats can increase the vulnerability of extirpation.
In the BRNHA, the Whitehorse population appears to be more vulnerable to harvest than the Three Fingers population due to accessibility and the spatial distribution of goats in the Whitehorse home range area. Collared mountain goats on Whitehorse had more locational data close to roads and trails and 96% of location fixes occurred inside the harvest area. State harvest data indicate that mountain goats are being harvested in the vicinity of trails primarily from the Whitehorse population (Washington Department of Fish and Wildlife unpublished data).